fieldsLinker.css

.fieldsLinker div {
    font-weight: bold;
}

.fieldsLinker ul {
    list-style: none;
    margin-left: 0px;
    padding-left: 0px;
    font-weight: normal;
}

tr td  {
    padding-left: 10px;
}

tr td:not(:last-child)  {
    border-right: 1px solid grey;
}

.fieldsLinker li {
    border: solid 1px grey;
    padding: 5px 2px 5px 8px;
    margin-top: 7px;
    margin-bottom: 8px;
    user-select: none;
    -moz-user-select: none;
    -webkit-user-select: none;
    -ms-user-select: none;
    cursor: pointer;
    background-color: #fff;
    background: linear-gradient(#ffffff, #e9e9e9);
    color: black;
    border-radius: 0px;
    text-overflow: ellipsis;
    overflow: hidden;
}

.fieldsLinker li.selected {
    -webkit-filter: invert(100%);
    filter: invert(100%);    
}

.fieldsLinker li[data-mandatory='true'] {
    background-color: #D7504C;
    background: linear-gradient(#D7504C, #C12F2B);
    color: white;
}

.fieldsLinker li.inactive {
    opacity: 0.5;
}

.fieldsLinker li.linkOver {
    border: solid 2px transparent; /*plus 1px*/
    padding: 4px 1px 4px 7px; /* minus 1px*/
}